Dose-response effects of colchicine and vinblastine on unimpeded eruption rates of the rat mandibular incisor

A comparison between a conventional optical method and image-analysis for measuring the unimpeded eruption rate of the rat mandibular incisor

The impeded/unimpeded eruption rates of the rat incisor have been much studied. The most commonly used optical microscopic method, which has inherent weaknesses, was compared here with an image-analysis method to measure the eruption rate of the mandibular incisor. The study also evaluated the incisal edge as a reference point for the measurement of the unimpeded eruption rate, and the frequency of shortening the mandibular incisor. The image-analysis method was found to be a simple and reliable technique that could replace the optical method. There was no significant difference between the data from the two methods; their kappa coefficients were similar at the 0.99 level. It was concluded that shortening the incisor in the measurement of the unimpeded eruption rate should be done at least every 48 h, and that the incisal edge of the shortened incisor can be used as the reference point for that measurement.

The effect of lead on the eruption rates of incisor teeth in rats

The effects of lead on the continuously erupting rat incisors under normo-, hyper- and hypofunctional conditions were investigated. Left lower incisors of 20 rats were rendered unimpeded (hypofunctional) by cutting them out of occlusion every 2 days; the right lower incisors of these rats were considered hyperfunctional. Measurements on normally growing teeth (normofunctional) were carried out in a group of ten rats whose teeth were not cut but only marked every 2 days. On day 7 of the experiment, half of the rats from these two groups were given a single intraperitoneal injection of lead acetate (40 mg/kg), and the other half received sodium acetate (22 mg/kg). Another group of 15 rats was used to obtain blood samples for lead determination 1 h, and 10, 20, and 30 days after lead administration. Animals were killed on day 32. Hypofunctional incisors from lead-treated rats erupted more slowly than control ones (P<0.05). These results show a previously unreported toxic effect of heavy metals.

Disturbed enamel mineralization in a rat incisor model

Possession of full-thickness hard enamel appears to be one of the indispensable life-saving characteristics of rats. Previous studies by Suga and his colleagues and by others demonstrated that various types of malformation are evoked in continuously erupting rat incisors. In the current report, we directed our effort to oversee various types of enamel malformation caused experimentally in rat incisors. We surveyed the specimens collected by Suga and his colleagues, as well as specimens we obtained. From the results, it is conceivable that perturbation of the programmed sequential events during enamel development is a major factor in the establishment of enamel malformation. Animal studies with either 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) or a multidentate phosphonic acid (EDTPO) confirmed that dentin mineralization provides a certain inductive effect on the secretion of enamel matrix and subsequent enamel crystallization. Our recent studies using anti-microtubular agents led to the conclusion that the acceleration of mineralization in outer enamel is a type of enamel malformation, most likely due to disruption of the cellular regulation of calcium transport under severe toxic regimens. In future work, experimental approaches combining measurements of kinetic factors with static observation of enamel lesions are required before we can gain a comprehensive understanding of the pathogenesis of disturbed enamel mineralization. The kinetic factors to be considered include the rates of tissue apposition and tooth eruption which determine the total volume of tooth substance formed, and the rate of mineral accretion. Furthermore, information as to the composition, crystallinity, solubility, and mechanical properties of enamel defects is needed before we can assess the susceptibility of teeth having those lesions to caries and other physico-chemical attacks in the oral environment.

Accelerated eruption of rat lower incisor. Relationship between impeded and unimpeded eruption rates, rate of attrition, tooth length, and production of dentin and enamel

The present investigation studies the effects of persistently cutting one lower rat incisor out of occlusion. Within four days, the rate of eruption of the cut (unimpeded) incisor increased to 216% and that of the uncut (impeded) contralateral to 136% of the baseline rate. While the former remained high, the latter decreased gradually to about 90% within three weeks. The rate of attrition of the impeded incisor increased to 233% of the baseline rate within two days, then fell abruptly, and remained at a slightly lower level than the rate of eruption. Accordingly, the length of the erupted part of the impeded incisor decreased initially, but increased gradually after about four days. Measurements made on SEM micrographs of the series of transverse tooth segments obtained when cutting the incisor out of occlusion, showed that growth-related increase in mesiodistal tooth width was arrested from the 10th segment, dentin thickness decreased gradually to about 50% in the 12th segment, and enamel thickness, after an initial increase, decreased to about 80% in the 11th segment. The present study provides experimental evidence that accelerated eruption affects morphogenesis and histogenesis of the rat lower incisor. An impeded incisor, especially the contralateral, may not serve as an ideal control.

The effect of vinblastine on the incorporation of [3H]-glycine into proteins of the periodontal ligament of impeded and unimpeded mouse incisors

The effect of vinblastine on the protein metabolism of the periodontal ligament of impeded and unimpeded mouse incisors was studied by [3H]-glycine labelling and radioautography. The silver-grain concentration was determined in areas adjacent to the tooth, areas adjacent to bone and, as an internal control, in the dentine matrix. From 1 to 12 h there was no difference between treated and control animals; thus the drug did not alter protein biosynthesis. Later, the silver-grain concentration was significantly higher in areas adjacent to both bone and tooth in vinblastine-treated animals, suggesting a longer half-life of the labelled proteins. No significant differences between normal or unimpeded erupting incisors of both groups were detected. Dentine matrix showed a possibly higher re-utilization of the labelled amino acid in vinblastine-treated animals. The amount of labelled protein removed by collagenase was similar in both groups, while the concentration of grains due to collagenase-resistant proteins was significantly higher in treated animals, particularly at 96 h after the injection of labelled glycine. The relation between the increased amount of non-collagenous proteins in the periodontal ligament and the decrease in the rate of eruption caused by vinblastine was not established. However, among these proteins, fibronectin and proteoglycans are thought to be important factors in tooth eruption.

The effects of cytoskeletal inhibitors on the collagen gel contraction by dog periodontal ligament fibroblasts in vitro

Periodontal ligament fibroblasts (PLF) were incorporated into small collagen gel discs (100 microliters, dia 10.0 mm), cultured in media containing various concentrations of cytochalasin D or colchicine and the diameters of the discs then measured. Cytochalasin D (3.1-800 nM) inhibited contraction of the gel discs in a dose-dependent manner and 800 nM of cytochalasin D completely inhibited contraction. This complete inhibition was still observed when cell density in the gel was increased. Although colchicine at a concentration of 0.98-15.7 nM also inhibited the contraction in a dose-dependent manner, contraction at 50% of the control level was still observed in the presence of a high concentration (0.25 mM, 100 micrograms/ml). These results strongly indicate that actin filaments are more intimately involved in PLF-mediated collagen gel contraction than microtubules. Although it is suggested that PLF are involved in tooth eruption, earlier studies have shown that microtubule inhibitors inhibit eruption of rat incisors whereas the microfilament inhibitor, cytochalasin B, has no effect. Thus, the PLF theory alone seems insufficient to explain the mechanism of tooth eruption.

The effects of colchicine or vinblastine on the blood calcium level in rats

In order to clarify how microtubule inhibitors induce hypocalcemia, rats were injected with intravenous colchicine (1 mg/kg) or vinblastine (2 mg/kg). The blood calcium levels decreased rapidly, and the minimum values, reached 4 h after the injection, were 7.55 +/- 0.70 mg/100 ml (mean +/- S.D., P < 0.001) for colchicine and 7.61 +/- 0.17 mg/100 ml (P < 0.001) for vinblastine. At 24 h, these values returned to the normal range (10.13 +/- 0.42 mg/100 ml). The blood calcium values in rats fed a low calcium diet and in thyroparathyroidectomized rats were also reduced by colchicine. The incorporation of blood 45Ca into bone was reduced by the injection of colchicine. Histologically, the bone cells of rats injected with either drug were severely damaged 8 h after the injection. These results indicate that hypocalcemia may be mediated by interference with the regulatory mechanisms of bone cell calcium homeostasis, and that the destruction of microtubules may be closely related to the development of the hypocalcemia.

Effect of colchicine on iron transport during stages of maturation and enamel pigmentation in rat incisor enamel: an autoradiographic study using 55Fe

An autoradiographic study on rats was carried out with 55Fe and colchicine in order to investigate the Arole of microtubules in the iron transport process from rat incisor ameloblasts to the enamel surface. In the control rats injected with 55Fe, autoradiographic silver grains were distributed over the ameloblasts during the whole stage of enamel maturation and over the enamel surface at the enamel pigmentation stage. After the colchicine injection, the area of ameloblasts with smooth distal cell membranes increased in the maturation stage. These ameloblasts were heavily injured, and the iron-containing pigment was released from the cell. The number of silver grains decreased in these ameloblasts. However, the silver grains increased in the area of ameloblasts with ruffled distal cell membranes. At the enamel pigmentation stage, the silver grains over the ameloblasts increased, and those over the enamel surface were reduced. The accumulation and dislocation of the iron-containing pigment was noted in the ameloblasts at this stage. Lumicolchicine injection did not affect the grain distribution. These findings suggest that microtubules regulate the transport and secretion process of iron in rat incisor ameloblasts.

Effect of vinblastine on the cell cycle and migration of ameloblasts of mouse incisors as shown by autoradiography using 3H-thymidine

The effects of vinblastine on the cell cycle and the migration of ameloblasts were studied in the lower incisors of mice by labelling the cells with 3H-thymidine ([3H]TdR) and radioautography. A group of mice received 2 micrograms/g of body weight vinblastine intraperitoneally and 6 hr after these animals and those of a control group were injected with 1 microCi/g body weight of [3H]TdR, and sacrificed at time intervals from 0.75 hr to 15 days. The generation time of ameloblasts in the progenitor compartment was 14.8 hr in animals treated with vinblastine and 17 hr in the controls, using the FLM curve method; with the grain dilution method the duration was respectively 29.25 hr and 25.96 hr. The thymidine labelling index of the treated animals was 50% higher than the controls. The velocity of ameloblast migration, determined either by the displacement of the most incisally labelled cell or by the grain dilution method, was lower in the experimental group (2.48 cell positions/hr and 9.18 microns/hr respectively) as compared with the control (3.21 cell positions/hr and 18.88 microns/hr respectively). The results on the ameloblast production rate are contradictory but the slowing down in the velocity of cell migration is compatible with a decrease of the rate of cell production in the progenitor compartment as a vinblastine effect.

Recovery of the dental and periodontal tissues of the rat incisor following application of continuous intrusive loads: a long-term study

The present investigation deals with the functional recovery of the rat incisor periodontium following application of optimal intrusive loads for a period of 2 weeks and addresses the relationship between function and integrity of dental and periodontal tissues. The daily rate of eruption served as an indicator of the functional capacity of the rat periodontal ligament (PDL), while the condition of the PDL was evaluated by means of serial histologic sections. The left mandibular incisors of thirteen experimental and seven control rats were shortened to prevent occlusion, and calibrated loads of 19 +/- 1.6 grams were applied to the teeth of the experimental animals. Following removal of the springs, the daily rate of eruption of all teeth was measured during a recovery period of 80 days. In all experimental animals, prolonged impairment of the eruptive potential had occurred: In 50% the rate of eruption was fully restored 8 weeks after removal of the loads, and in these animals the histologic evaluation showed an almost normal PDL. In the remaining 50% gross impediment in the eruption rate persisted throughout the entire experimental period. The intratissue forces operating during the recovery period had sufficient strength to cause a degree of periodontal injury equivalent to that ensuant on direct loading. Extensive newly developed necrotic lesions were evident in the initially stretched mesial PDL. Areas of dentin resorption, denuded cementum, and injured enamel appeared a considerable time after load removal. Periodontal injury included disorientation and loss of attachment of collagen fibers, presence of scarlike tissue, and infiltration of inflammatory cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of colchicine and hydrocortisone on unimpeded eruption rates of root-resected mandibular incisors of rats

A single injection of colchicine and daily injections of hydrocortisone have opposite effects on tooth eruption, respectively causing marked reduction and marked increase in unimpeded eruption rates in the root-resected incisors of rats. Unimpeded eruption rates of both root-resected and normal, non-resected, incisors responded identically to these two drugs, providing support for the view that the eruptive process following root resection is physiological. It was not possible to obtain direct evidence relating to either the hydrostatic pressure or the periodontal fibroblast hypotheses of tooth eruption; the drugs used to affect the eruption rates of resected rat incisors could also affect either the tissue hydrostatic pressure or the motility or contractibility of periodontal fibroblasts or both.

An in-vitro model for tooth eruption utilizing periodontal ligament fibroblasts and collagen lattices

An in-vitro model that simulates tooth eruption was devised to determine the possible role of periodontal ligament fibroblasts (PLF) in providing a major force for eruption. The model consisted of agarose-coated wells in multiwell tissue-culture plates to which wire mesh was attached at the rim and a slice of demineralized root was attached to the floor. When the wells were filled with a collagen lattice containing PLF, the lattice contracted and elevated the root slice. The root slice in models that were unattached at the rim was not elevated. Cultures without cells did not contract and root slices were not elevated. Elevation was inhibited by cytochalasin D and Colcemid. Histologically, cultures that had elevated showed orientated cells and collagen fibres. The results suggest that PLF may be capable of generating forces that are sufficient to produce tooth eruption.

The effect of a microfilament-disrupting drug, cytochalasin B, on 6-hourly and daily eruption rates of the rat mandibular incisor

The drug did not affect 6-hourly and daily eruption rates of the unimpeded mandibular incisor of the rat. It is suggested that the tooth eruption is not inhibited by the disruption of microfilaments because the disruption was not associated with the motility of the cells and/or that the motility of the cells is not associated with the motive force of tooth eruption. Further studies may be necessary to confirm that the effects of cytochalasin B are on both microfilaments and motility of the periodontal fibroblasts.